Workpiece placement apparatus and processing apparatus

ABSTRACT

A placement apparatus for placing a workpiece is provided. The placement apparatus includes a stage on which a workpiece can be placed in a processing vessel; an edge ring including a locking part which is disposed on the stage so as to surround a periphery of the workpiece; a conductive connecting member connected with the edge ring at the locking part; and a first contacting member configured to cause the edge ring to contact the stage, while the edge ring is connected with the connecting member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 16/293,788 filed on Mar. 6, 2019, which is based on and claimspriority to Japanese Patent Application No. 2018-041231 filed on Mar. 7,2018. The entire contents of these applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to a workpiece placementapparatus and a processing apparatus.

2. Description of the Related Art

In a processing chamber of a processing apparatus, an edge ring isdisposed on a stage so as to surround a periphery of a wafer, in orderto direct plasma toward a surface of the wafer. During plasmaprocessing, as the edge ring is exposed to plasma, the edge ring becomesworn.

As a result, because a level difference may occur to with respect asheath generated on an edge ring and a sheath generated on a wafer andan incident angle of ions may be tilted at an edge of the wafer, tiltingmay occur on an etching profile. Also, as an etching rate at the edge ofthe wafer may vary, an etching rate in a wafer may become uneven.Accordingly, when an edge ring is worn to a certain amount, the edgering is replaced with a new one. However, a time for replacing an edgering is one of factors degrading productivity.

In order to alleviate the problem, a technique for controllingdistribution of an etching rate of a surface by applying DC (directcurrent) voltage to an edge ring from a DC power source has beenproposed (see Patent Documents 1 to 7, for example).

When DC voltage is applied to an edge ring, it is important that theedge ring is stably in contact with a base member of a stage on whichthe edge ring is placed. By the edge ring being in contact with the basemember stably, electric potential of the edge ring becomes equal toelectric potential of the base member, and a thickness of a sheath onthe edge ring can be controlled precisely.

CITATION LIST Patent Document

-   [Patent Document 1] Japanese Laid-open Patent Application    Publication No. 2014-007215-   [Patent Document 2] U.S. Pat. No. 7,572,737-   [Patent Document 3] U.S. Pat. No. 9,536,711-   [Patent Document 4] U.S. Pat. No. 9,412,579-   [Patent Document 5] Japanese Laid-open Patent Application    Publication No. 2004-079820-   [Patent Document 6] Japanese Laid-open Patent Application    Publication No. 2006-080375-   [Patent Document 7] Japanese Laid-open Patent Application    Publication No. 2006-245510

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a placement apparatusfor placing a workpiece is provided. The placement apparatus includes astage on which a workpiece can be placed in a processing vessel; an edgering including a locking part which is disposed on the stage so as tosurround a periphery of the workpiece; a conductive connecting memberconnected with the edge ring at the locking part; and a first contactingmember configured to cause the edge ring to contact the stage, while theedge ring is connected with the connecting member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a processing apparatusaccording to the present disclosure;

FIG. 2A and FIG. 2B are diagrams illustrating a variation of an etchingrate and occurrence of tilting that are caused by abrasion of an edgering;

FIG. 3A and FIG. 3B are diagrams illustrating a problem caused by anapplied force and by thermal expansion at a contacting part;

FIG. 4A and FIG. 4B are diagrams illustrating examples of contactingstructures of an edge ring and a stage according to a first embodiment;

FIG. 5 is a diagram illustrating an example of a contacting structure ofthe edge ring and the stage according to a second embodiment;

FIG. 6A is a diagram illustrating an example of a contacting structureof the edge ring and the stage according to a third embodiment;

FIG. 6B is a diagram illustrating an example of a second contactingpart; and

FIG. 7 is a diagram illustrating an example of a method of applying DCvoltage according to a modified example of the first, second, or thirdembodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the drawings. Note that in the following descriptionsand the drawings, elements having substantially identical features aregiven the same reference symbols and overlapping descriptions may beomitted.

[Processing Apparatus]

First, an example of a processing apparatus 1 according to the presentdisclosure will be described with reference to FIG. 1. FIG. 1 is adiagram illustrating a cross section of the processing apparatus 1according to the present disclosure. The processing apparatus 1according to the present disclosure is a processing apparatus of areactive ion etching (RIE) type.

The processing apparatus 1 includes a cylindrical processing vessel 10formed of metal, such as aluminum or stainless steel. The inside of theprocessing vessel 10 is a processing chamber for performing a plasmaprocess such as plasma etching or plasma CVD. The processing vessel 10forms a processing space for applying a process to a semiconductor waferW which is an example of a workpiece (hereinafter, a semiconductor waferW may also be referred to as a “wafer W”). The processing vessel 10 isgrounded.

A disc shaped stage 11 is provided in the processing vessel 10. Thestage 11 is used for placing a wafer W. The stage 11 includes anelectrostatic chuck 25. The stage 11 is supported by a cylindricalsupporting member 13 that extends upward from the bottom of theprocessing vessel 10, via a cylindrical holding member 12 formed ofaluminum oxide (Al₂O₃).

The electrostatic chuck 25 includes a base 25 c formed of aluminum, anda dielectric layer 25 b disposed on the base 25 c. An attractingelectrode 25 a made from conductive film is embedded in the dielectriclayer 25 b. A direct current (DC) power source 26 is connected to theattracting electrode 25 a via a switch 27. The electrostatic chuck 25generates electrostatic force (Coulomb force) by DC voltage applied fromthe DC power source 26 to the attracting electrode 25 a, and a wafer Wis attracted to and held by the electrostatic chuck 25 by the generatedelectrostatic force.

At outer circumferences of the electrostatic chuck 25 and the wafer W onthe base 25 c, an edge ring 30 is disposed. The edge ring 30 is madefrom Si or SiC. An outer circumference of the electrostatic chuck 25 andan outer circumference of the edge ring 30 are covered by an insulatorring 32.

A first high frequency power source 21 is connected to the stage 11 viaa matching unit 21 a. The first high frequency power source 21 supplies,to the stage 11, high frequency electric Power of a first frequency(such as a frequency of 13 MHz) for generating plasma or for RIB(hereinafter, the high frequency electric power of the first frequencymay also be referred to as “first high frequency electric power”). Also,a second high frequency power source 22 is connected to the stage 11 viaa matching unit 22 a. The second high frequency power source 22 supplieshigh frequency electric power of a second frequency lower than the firstfrequency (such as a frequency of 3 MHz) for generating bias voltage(hereinafter, the high frequency electric power of the second frequencymay also be referred to as “second high frequency electric power”).Thus, the stage 11 also functions as a lower electrode.

A variable DC power source 28 is connected to an electric wire 21 b viaa switch 29. A blocking capacitor 23 is provided between a connectionpoint of the variable DC power source 28 on the electric wire 21 b andthe first high frequency power source 21. The blocking capacitor 23 isused to block DC voltage applied from the variable DC power source 28,so that DC voltage is not applied to the first high frequency powersource 21. By the DC voltage applied from the variable DC power source28, voltage is applied to the edge ring 30.

In the base 25 c, a coolant chamber 31 of an annular shape, whichextends in a circumferential direction, is provided. From a chillerunit, coolant at a predetermined temperature, such as cooling water, issupplied to the coolant chamber 31, and the coolant circulates in thecoolant chamber 31 via pipes 33 and 34, in order to cool theelectrostatic chuck 25 and the wafer W.

To the electrostatic chuck 25, a heat transmitting gas supply unit 35 isconnected via a gas supply line 36. The heat transmitting gas supplyunit 35 supplies heat transmitting gas to a space between the uppersurface of the electrostatic chuck 25 and a bottom surface of the waferW. Gas having good heat conductivity, such as He gas, may preferably beused as a heat transmitting gas.

Between a side wall of the processing vessel 10 and the cylindricalsupporting member 13, an exhaust path 14 is formed. At an entrance ofthe exhaust path 14, an annular baffle plate 15 is provided. At a bottomof the exhaust path 14, an exhaust port 16 is provided. An exhaustdevice 18 is connected to the exhaust port 16 via an exhaust pipe 17.The exhaust device 18 includes a vacuum pump, and can reduce pressure ofa processing space in the processing vessel 10 to a desirable quality ofvacuum. Also, the exhaust pipe 17 includes an automatic pressure controlvalve (hereinafter referred to as an “APC”) of a variable butterflyvalve. The APC automatically controls pressure in the processing vessel10. Further, a gate valve 20 is provided at the side wall of theprocessing vessel 10, which is used for opening and/or closing aloading/unloading port 19 for the wafer W.

A gas shower head 24 is mounted to a ceiling of the processing vessel10. The gas shower head 24 includes an electrode plate 37, and anelectrode supporting member 38 that detachably supports the electrodeplate 37. The electrode plate 37 includes a large number of gas holes 37a. A buffer chamber 39 is provided in the electrode supporting member38. The buffer chamber 39 includes a gas inlet port 38 a, and a processgas supply unit 40 is connected to the gas inlet port 38 a via a gassupplying pipe 41. Further, at a periphery of the processing vessel 10,annular magnets 42 are provided coaxially.

Each component of the processing apparatus 1 is connected to a controlunit 43. The control unit 43 controls each of the components of theprocessing apparatus 1. Examples of the component include the exhaustdevice 18, the matching units 21 a and 22 a, the first high frequencypower source 21, the second high frequency power source 22, the switches27 and 29, the DC power source 26, the variable DC power source 28, theheat transmitting gas supply unit 35, and the process gas supply unit40.

The control unit 43 includes a CPU 43 a and a memory 43 b. The CPU 43 areads out a control program for the processing apparatus 1 and a processrecipe that are stored in the memory 43 b, and executes the controlprogram and the process recipe to cause the processing apparatus 1 toperform a predetermined process such as etching.

For example, when an etching process is performed in the processingapparatus 1, the gate valve 20 is opened first. Next, a wafer W isloaded into the processing vessel 10 and placed on the electrostaticchuck 25. Subsequently, DC voltage from the DC power source 26 isapplied to the attracting electrode 25 a to attract the wafer W to theelectrostatic chuck 25, and DC voltage output from the variable DC powersource 28 is applied to the base 25 c, to apply DC voltage to the edgering 30. Also, heat transmitting gas is supplied to the space betweenthe electrostatic chuck 25 and the wafer W. Next, process gas isintroduced inside the processing vessel 10, and pressure in theprocessing vessel 10 is reduced by the exhaust device 18 and the like.Further, first high frequency electric power and second high frequencyelectric power are supplied to the stage 11 from the first highfrequency power source 21 and the second high frequency power source 22respectively.

In the processing vessel 10 of the processing apparatus 1, a magneticfield of a horizontal direction is created by the magnets 42, and an RFelectric field of a vertical direction is generated by high frequencyelectric power applied to the stage 11. Because of the generatedmagnetic field and the generated electric field, the process gasdischarged from the gas shower head 24 is changed to plasma, and a givenplasma process is applied to the wafer W by radicals or ions in theplasma.

[Abrasion of Edge Ring]

Next, a change of sheath, a variation of an etching rate, and occurrenceof tilting, which are caused by abrasion of the edge ring 30, will bedescribed with reference to FIGS. 2A and 2B. As illustrated in FIG. 2A,a thickness of the edge ring 30 is designed such that an upper surfaceof a wafer W and an upper surface of the edge ring 30 are at the samesame height, when the edge ring 30 is new. In such a state, duringplasma processing, the sheath above the wafer W and the sheath above theedge ring 30 are at the same height, and an incident angle of ions fromplasma above the wafer W and the edge ring 30 is vertical. As a result,an etching profile of a hole or the like formed on the wafer W becomesvertical, and an etching rate becomes uniform on an entire surface ofthe wafer W.

However, by the plasma processing being performed, as the edge ring 30is exposed to plasma, the edge ring 30 abrades. Thus, as illustrated inFIG. 2B, because the height of the upper surface of the edge ring 30becomes lower than the height of the upper surface of the wafer W, thesheath above the edge ring 30 becomes lower than the sheath above thewafer W in height.

At an edge of the wafer W in which a height difference of sheath occurs,an incident angle of ions becomes slanted, and tilting may occur in anetching profile. In addition, an etching rate at the edge of the wafer Wvaries, and the etching rate may become uneven on the surface of thewafer W.

However, in the processing apparatus 1 according to the presentdisclosure, as DC voltage output from the variable DC power source 28 isapplied to the edge ring 30 to control thickness of a sheath, a sheathabove the wafer W and a sheath above the edge ring 30 can be made to beat the same height during plasma processing. Accordingly, distributionof an etching rate on a surface and tilting can be controlled.

When DC voltage is applied to the edge ring 30, it is important that theedge ring 30 and the base member 25 c are stably maintained at the sameelectric potential. Thus, one conceivable structure is that an elasticspiral tube 59 of a conductive material is disposed on the upper surfaceof the base member 25 c, as illustrated in FIG. 3A, in order to causethe edge ring 30 to contact the base 25 c.

However, in this structure, because of elastic force of the spiral tube59, the edge ring 30 may be lifted and may depart from the base member25 c. Thus, in this structure, DC voltage applied to the base member 25c is not conducted to the edge ring 30 sufficiently, and it is difficultto maintain the edge ring 30 and the base member 25 c at the sameelectric potential.

Another conceivable structure is that an edge ring 30 having an L-shapedcross section is used and that a spiral tube 59 is provided between aside wall of the edge ring 30 and a side wall of the base member 25 csuch that the spiral tube 59 is pressed to the edge ring 30 by the basemember 25 c. However, in this structure, because the edge ring 30 andthe base member 25 c may be made from different materials, an amount ofthermal expansion (or an amount of thermal contraction) of the edge ring30 in a radial direction may become different from an amount of thermalexpansion (or an amount of thermal contraction) of the base member 25 cin a radial direction, if temperature of the electrostatic chuck 25 ischanged in accordance with process conditions. Because of the differenceof an amount of thermal expansion (or contraction) of each of themembers (the edge ring 30 and the base member 25 c), a case may occur inwhich the spiral tube 59 does not contact the edge ring 30. Therefore,in this structure, DC voltage applied to the base member 25 c is notconducted to the edge ring 30 sufficiently, and it is difficult tomaintain the edge ring 30 and the base member 25 c at the same electricpotential.

The above described phenomenon that the edge ring 30 departs from thebase member 25 c occurs because of size differences of members of theprocessing apparatus 1 (such as the edge ring 30 and the base member 25c), or because of a difference of an amount of thermal expansion (orcontraction) of each of the members caused by heat from plasma. It isdifficult to eliminate the size differences of the members, or thedifference of an amount of thermal expansion (or contraction) of each ofthe members.

Thus, in the present disclosure, the processing apparatus 1 having astructure in which the edge ring 30 is stably in contact with the stage11 is provided. In the following, contacting structures according to afirst to third embodiments will be described with reference to FIGS. 4Ato 6B.

First Embodiment

[Contacting Structure of Edge Ring and Stage]

First, an example of a contacting structure of the edge ring 30 and thestage 11 according to a first embodiment will be described withreference to FIG. 4A and FIG. 4B. Note that, in the present disclosure,a structure of the edge ring 30 and the stage 11 (specifically, the basemember 25 c of the stage 11) in which the edge ring 30 and the stage 11are connected with each other in a conductive state is referred to as a“contacting structure”. Also, a state in which the edge ring 30 is(directly or indirectly) connected with the stage 11 in a conductivestate is referred to as “contact”. FIG. 4A is a diagram illustrating anexample of a contacting structure of the edge ring 30 and the stage 11according to the first embodiment. FIG. 4B is a diagram illustrating anexample of a contacting structure of the edge ring 30 and the stage 11according to a modified example of the first embodiment. First, thecontacting structure according to the first embodiment will bedescribed.

As illustrated in FIG. 4A, a locking part 30 a is formed in the edgering 30 according to the first embodiment. The locking part 30 a is arecess provided at a position close to an outer circumference of theedge ring 30. An opening of the recess (locking part 30 a) faces acenter axis of the edge ring 30, and the recess is formed toward anouter circumference of the edge ring 30. The locking part 30 a (recess)is provided along an entire circumference of the edge ring 30.

In the first embodiment, a placement apparatus (including the stage 11and the edge ring 30) includes a first contacting member 51, aconductive connecting member 50, and a second contacting member 52. Inthe locking part 30 a, the first contacting member 51 pushes the edgering 30 toward the base member 25 c, while the edge ring 30 is caused tobe connected with the connecting member (specifically, the edge ring 30is pushed to the connecting member 50 by the first contacting member51). The first contacting member 51 is made from an elastic andconductive material, and is a spiral tube, for example. That is, thefirst contacting member 51 functions as a member for causing the edgering 30 and the base member 25 c to contact stably. The first contactingmember 51 may be a member configured to cause the edge ring 30 tocontact the stage 11, while the edge ring 30 is caused to physicallytouch the connecting member 50.

The connecting member 50 is a member having an L-shaped cross section,and consists of a horizontal part 50 a and a vertical part 50 b. Thehorizontal part 50 a of the connecting member 50 is inserted in thelocking part 30 a (recess). The horizontal part 50 a is inserted in thelocking part 30 a with a clearance, so that the horizontal part 50 a canmove in a radial direction when a difference between amounts of thermalexpansion (or contraction) of the edge ring 30 and the base member 25 coccurs. Thus, because of the locking part 30 a, the edge ring 30 isconnected with the connecting member 50.

The first contacting member 51 is disposed at a recess formed on a partof the horizontal part 50 a inserted in the locking part 30 a. Becauseof the structure, the first contacting member 51 can push the edge ring30 toward the base member 25 c. By the force pushing the edge ring 30toward the base member 25 c, force lifting the edge ring 30 in a heightdirection is cancelled, and the first contacting member 51 can conductelectricity between the edge ring 30 and the base member 25 c whileabsorbing an effect of thermal expansion. The recess of the horizontalpart 50 a may be formed such that an opening of the recess is present ona lower surface of the horizontal part 50 a, as illustrated in FIG. 4A.Alternatively, the recess of the horizontal part 50 a may be formed suchthat an opening is present on an upper surface of the horizontal part 50a. The first contacting member 51 is provided at the lower surface orthe upper surface of the horizontal part 50 a, depending on a locationof the recess.

The second contacting member 52 is provided at a position lower than thefirst contacting member 51, and is in contact with a recess provided ata side wall of the base member 25 c. The second contacting member 52 isa spiral tube, for example, and is made from an elastic and conductivematerial. The second contacting member 52 pushes the vertical part 50 bof the conductive connecting member 50. The vertical part 50 b extendsdownwards, from a level of the first contacting member 51. Because ofthe above described structure, electricity is stably conducted betweenthe edge ring 30 and the base member 25 c.

As described above, in the contacting structure according to the firstembodiment, the connecting member 50 is inserted in the locking part 30a which is the recess formed in the edge ring 30 toward an outercircumference of the edge ring 30, and the first contacting member 51 isprovided at a recess formed on a part of the connecting member 50inserted in the locking part 30 a. Because of this structure, force in aheight (vertical) direction applied to the edge ring 30 from the firstcontacting member 51 is cancelled, and the edge ring 30 is preventedfrom being lifted. Further, in the locking part 30 a, as the connectingmember 50 is configured to be moved in a radial direction in response toan occurrence of thermal expansion (or contraction), an effect ofthermal expansion is reduced. Thus, electricity is conducted withcertainty between the edge ring 30 and the base member 25 c.

In a case in which conductive material is partly disposed at an edgering in a circumferential direction, electrical bias occurs. On theother hand, in the present embodiment, as the first contacting member 51is a ring-shaped member, the first contacting member 51 is disposed atan entire circumference of the edge ring 30. Accordingly, the edge ring30 is uniformly contacted with the base member 25 c in the entirecircumference of the first contacting member 51. Thus, the edge ring 30and the base member 25 c are stably maintained at the same electricpotential.

As described above, in the present embodiment, force lifting the edgering 30 in a height direction is cancelled, and electricity is conductedwith certainty between the edge ring 30 and the base member 25 c whileabsorbing an effect of thermal expansion. Thus, the edge ring 30 isstably contacted with the base member 25 c.

As a result, because DC voltage from the variable DC power source 28 isapplied with certainty to the edge ring 30, a sheath above the edge ring30 can be precisely controlled during plasma processing, occurrence oftilting is suppressed, and uniformity of distribution of an etching rateon a surface improves. As a result, even if the edge ring 30 has abradedto a certain extent, a replacement cycle of the edge ring 30 can beextended by controlling DC voltage applied to the edge ring 30, andproductivity is increased.

However, instead of a ring-shaped member, multiple separate arc-shapedmembers may be used as the first contacting member 51. The secondcontacting member 52 may also be formed of multiple arc-shaped members(such as arc-shaped members 52 a, 52 b, and 52 c illustrated in FIG.6B), and each of the arc-shaped members may be disposed separately. Theconnecting member 50 may also be formed of multiple arc-shaped members.Note that the multiple arc-shaped members forming the second contactingmember 52 are not required to be disposed separately, and may beconnected with each other. Similarly, the multiple arc-shaped membersforming the connecting member 50 are not required to be disposedseparately, and may be connected with each other. Alternatively, thesecond contacting member 52 and the connecting member 50 are notnecessarily formed of multiple separate members.

In the first embodiment, by the first contacting member 51 beingprovided, electricity can be conducted between the edge ring 30 and thebase member 25 c via the connecting member 50. Thus, the secondcontacting member 52 is not required to be provided. Also, the secondcontacting member 52 may not be a conductive member. However, in orderthat the connecting member 50 is contacted with the base member 25 cmore stably, it is preferable that the second contacting member 52 isprovided.

Modified Example of First Embodiment

Next, the contacting structure of the edge ring 30 and the stage 11according to the modified example of the first embodiment, which isillustrated in FIG. 4B, will be described. In the following, adifference between the contacting structure according to the modifiedexample and the contacting structure according to the first embodimentis mainly described.

In the modified example of the first embodiment, the connecting member50 is fixed to the base member 25 c with a screw 61. Accordingly, theconnecting member 50 is kept in contact with the base member 25 c morestably, and the edge ring 30 can be contacted with the base member 25 cstably. In the modified example of the first embodiment, as the screw 61is disposed such that the screw 61 penetrates an inside of a cylindricalcollar 60 provided between the insulator ring 32 and the base member 25c, the screw 61 is less likely to be affected by thermal expansion. Thescrew 61 is an example of a fixing member for fixing the connectingmember 50 to the base member 25 c, and the fixing member is not limitedto the screw 61.

In the modified example of the first embodiment, by the first contactingmember 51 being provided, electricity can be conducted between the edgering 30 and the base member 25 c via the connecting member 50, similarto the first embodiment. Thus, Thus, the second contacting member 52 isnot required to be provided. Also, the second contacting member 52 maynot be a conductive member. However, in order that the connecting member50 is contacted with the base member 25 c more stably, it is preferablethat the second contacting member 52 is provided.

Second Embodiment

[Contacting Structure of Edge Ring and Stage]

Next, an example of a contacting structure of the edge ring 30 and thestage 11 according to a second embodiment will be described withreference to FIG. 5. FIG. 5 is a diagram illustrating the example of thecontacting structure of the edge ring 30 and the stage 11 according tothe second embodiment.

In the contacting structure according to the second embodiment, by thefirst contacting member 51, a connecting member 53, and the secondcontacting member 52, the edge ring 30 is contacted with the base member25 c stably.

The connecting member 53 according to the second embodiment is aring-shaped member, which is made from conductive material such asaluminum, and is inserted in a recess formed at a side surface of theinsulator ring 32, which faces a boundary of outer circumferences of theedge ring 30 and the base member 25 c.

The contacting structure according to the second embodiment is alsodesigned such that the edge ring 30 is prevented from being lifted byelastic force of the first contacting member 51. Specifically, a recessis formed on an upper end of an inner circumference of the connectingmember 53, which faces the outer circumference of the edge ring 30. Thefirst contacting member 51 is disposed at the recess, and pushes theedge ring 30 from the outer circumference while contacting the insulatorring 32 and the connecting member 53. According to the structure,because the first contacting member 51 pushes the edge ring 30 in aradial direction, the edge ring 30 is not lifted by the elastic force ofthe first contacting member 51.

Also, in the second embodiment, the second contacting member 52 isprovided at a position lower than the first contacting member 51, and isin contact with a recess provided at a side wall of the base member 25c. Also, in the second embodiment, the first contacting member 51 is aring-shaped member, and the first contacting member 51 is disposed at anentire circumference of the edge ring 30. Accordingly, the edge ring 30is uniformly contacted with the base member 25 c in the entirecircumference of the first contacting member 51. Thus, the edge ring 30and the base member 25 c are stably maintained at the same electricpotential.

However, instead of a ring-shaped member, multiple separate arc-shapedmembers may be used as the first contacting member 51. The secondcontacting member 52 may also be formed of multiple arc-shaped membersas illustrated in FIG. 6B, and each of the arc-shaped members may bedisposed separately. The connecting member 53 may also be formed ofmultiple arc-shaped members. Note that the multiple arc-shaped membersforming the second contacting member member 52 are not required to bedisposed separately, and may be connected with each other. Similarly,the multiple arc-shaped members forming the connecting member 53 are notrequired to be disposed separately, and may be connected with eachother. Alternatively, the second contacting member 52 and the connectingmember 53 are not necessarily formed of multiple separate members.

As described above, the contacting structure according to the secondembodiment includes the edge ring 30, the base member 25 c, theconductive connecting member 53 provided around the outer circumferencesof the edge ring 30 and the base member 25 c, the first contactingmember 51 provided between the edge ring 30 and the connecting member 53which is configured to push the edge ring 30 from the outercircumference of the edge ring 30 to a direction away from theconnecting member 53, and the second contacting member 52 provided at aposition lower than the first contacting member 51, which is in contactwith the base member 25 c.

According to the structure, a difference of an amount of thermalexpansion of the edge ring 30 and an amount of thermal expansion of thebase member 25 c, which varies depending on process conditions, can beabsorbed, without applying force in a height direction to the edge ring30. Thus, electricity is conducted between the edge ring 30 and the basemember 25 c with certainty. In the second embodiment, electricity isconducted with certainty between the edge ring 30 and the base member 25c even with a simple structure. That is, the contacting structureaccording to the second embodiment makes maintenance of the processingapparatus 1 easier.

Note that, in the second embodiment, not only the first contactingmember 51 but also the second contacting member 52 are necessary, inorder to conduct electricity between the edge ring 30 and the basemember 25 c.

Third Embodiment

[Contacting Structure of Edge Ring and Stage]

Next, an example of a contacting structure of the edge ring 30 and thestage 11 according to a third embodiment will be described withreference to FIG. 6A. FIG. 6A is a diagram illustrating the example ofthe contacting structure of the edge ring 30 and the stage 11 accordingto the third embodiment. FIG. 6B is a diagram illustrating an example ofa second contacting member 52, in a case in which the second contactingmember 52 is formed of multiple separate members.

As compared with the contacting structure according to the secondembodiment, the contacting structure according to the third embodimentis different in that the first contacting member 51 is disposed at adifferent location, in that an edge ring 30 according to the thirdembodiment includes a locking part 30 b, and in that the contactingstructure according to the third embodiment includes a hook portion 54.

The first contacting member 51 according to the third embodiment isprovided between the edge ring 30 and the base member 25 c, and appliesforce to the lower surface of the edge ring 30 in a direction away fromthe base member 25 c. The locking part 30 b is a projection protrudingfrom a lower end of an outer circumference of the edge ring 30. By thelocking part 30 b being inserted into a recess formed on an inner sidewall of a connecting member 53, the edge ring 30 is anchored to theconnecting member 53. The locking part 30 b protrudes from the entireouter circumference of the edge ring 30, like a flange.

According to the above mentioned structure, although the firstcontacting member 51 applies elastic force to the edge ring 30 in aheight direction, the edge ring 30 is not lifted by the force of thefirst contacting member 51. Further, the second contacting member 52 isprovided at a position lower than the first contacting member 51, and isin contact with a recess provided at a side wall of the base member 25c. The hook portion 54 protrudes from the connecting member 53, and isembedded in the base member 25 c in a horizontal direction such that apart of an upper surface of the hook portion 54 touches a bottom surfaceof the second contacting member 52. Accordingly, by the elastic secondcontacting member 52, force in a downward direction is applied to theconnecting member 53 via the hook portion 54, and thereby the edge ring30 is prevented from being lifted.

In the third embodiment also, the first contacting member 51 is aring-shaped member, and the first contacting member 51 is disposed at anentire circumference of the edge ring 30. Accordingly, the edge ring 30is uniformly contacted with the base member 25 c in the entirecircumference of the first contacting member 51. Thus, the edge ring 30and the base member 25 c are stably maintained at the same electricpotential. However, instead of a ring-shaped member, multiple separatearc-shaped members may be used as the first contacting member 51.

As illustrated in FIG. 6B, the second contacting member 52 may also beformed of the three separate arc-shaped members 52 a, 52 b, and 52 c.After the arc-shaped members 52 a, 52 b, and 52 c are fitted to therecess in the base member 25 c, the arc-shaped members 52 a, 52 b, and52 c get connected with each other, by using parts for connection suchas screws, pins, or other connecting means. The number of arc-shapedmembers forming the second contacting member 52 is not limited to 3.That is, the second contacting member 52 may be formed of arc-shapedmembers of numbers other than 3. Alternatively, the second contactingmember 52 and the connecting member 53 are not necessarily formed ofmultiple separate members.

As described above, the contacting structure according to the thirdembodiment is designed such that the locking part 30 b protruding fromthe outer circumference of the edge ring 30 is formed on the edge ring30, and that the edge ring 30 is anchored to the connecting member 53 bythe locking part 30 b being inserted into a recess formed on an innerside wall of a connecting member 53. According to the structure, adifference of an amount of thermal expansion of the edge ring 30 and anamount of thermal expansion of the base member 25 c, which variesdepending on process conditions, can be absorbed, while cancelling forcein a height direction applied to the edge ring 30. Thus, electricity isconducted with certainty between the edge ring 30 and the base member 25c. In the third embodiment, electricity is conducted with certaintybetween the edge ring 30 and the base member 25 c even with a simplestructure. That is, the contacting structure according to the secondembodiment makes maintenance of the processing apparatus 1 easier.

In the third embodiment, by the first contacting member 51 beingprovided, electricity can be conducted between the edge ring 30 and thebase member 25 c via the connecting member 53. Thus, the secondcontacting member 52 is not required to be provided. However, in orderthat the connecting member 53 is contacted with the base member 25 cmore stably, it is preferable that the second contacting member 52 isprovided.

<Modified Example of Method of Applying DC Voltage>

In the processing apparatus 1 according to the first, second, or thirdembodiment described above, DC voltage output from the variable DC powersource 28 is applied to the edge ring 30 via the electric wire 21 b. Inthe following, a modified example of a method of applying DC voltage tothe edge ring 30 will be described with reference to FIG. 7.

In the modified example to be described below, a cylindrical shapedinsulating member 56 is disposed in a base member (which corresponds tothe base member 25 c according to the first to third embodiments) at atan inner position relative to the second contacting member 52, such thatan inner portion 25 c 1 of the base member is electrically separatedfrom an outer portion 25 c 2 of the base member. It is preferable thatthe insulating member 56 is provided at, but not limited to, the outerportion 25 c 2 of the base member. The insulating member 56 may bedisposed such that the inner portion 25 c 1 of the base member iselectrically separated from the outer portion 25 c 2 of the base member.

Also, in the modified example, a variable DC power source 55 which isdifferent from the variable DC power source 28 (in FIG. 1) is provided.By the variable DC power source 55, DC voltage can be applied to theedge ring 30. Specifically, the variable DC power source 55 is connectedto the outer portion 25 c 2 of the base member, and applies DC voltageto the outer portion 25 c 2 independent of the variable DC power source28 (in FIG. 1). The DC voltage applied to the outer portion 25 c 2 isalso applied to the edge ring 30 via the connecting member 50. Accordingto the structure, as thickness of a sheath can be controlled, a sheathabove a wafer W and a sheath above the edge ring 30 can be made to be atthe same height during plasma processing. Therefore, distribution of anetching rate on a surface and tilting can be controlled.

The variable DC power source 55 in the modified example is an example ofa DC voltage application unit connected to an outer region of the stage11. A method of applying DC voltage according to the modified example isapplicable to all of the first, second, and third embodiments.

Although the processing apparatus has been described in the aboveembodiments, a processing apparatus according to the present inventionis not limited to the above embodiments. Various changes or enhancementscan be made hereto within the scope of the present invention. Mattersdescribed in the above embodiments may be combined unless inconsistencyoccurs.

The present invention is applicable not only to a parallel-flat platetype dual-frequency apparatus illustrated in FIG. 1, but also to othertypes of apparatus, such as a capacitively coupled plasma (CCP) typeprocessing apparatus, an inductively coupled plasma (ICP) typeprocessing apparatus, a processing apparatus using a radial line slotantenna, a helicon wave plasma (HWP) type processing apparatus, anelectron cyclotron resonance plasma (ECR) type, or a surface wave plasmaprocessing apparatus.

In this specification, the semiconductor wafer W is referred to as anexample of a workpiece. However, the workpiece is not limited to thesemiconductor wafer. Examples of the workpiece may include various typesof substrates used in an LCD (Liquid Crystal Display) or a FPD (FlatPanel Display), a photomask, a CD substrate, or a printed circuit board.

1-3. (canceled)
 4. A placement apparatus for placing a workpiece in aprocessing vessel, the placement apparatus comprising: a stage on whichthe workpiece can be placed; an edge ring disposed on the stage so as tosurround a periphery of the workpiece; a conductive connecting memberprovided around outer circumferences of the edge ring and the stage; afirst contacting member provided between the edge ring and theconnecting member so as to be in contact with the connecting member andan outer circumference of the edge ring; and a second contacting memberprovided at a position lower than the first contacting member, so as tobe in contact with the stage.
 5. The placement apparatus according toclaim 4, wherein the first contacting member is a ring-shaped member andis provided at an entire circumference of the edge ring.
 6. Theplacement apparatus according to claim 4, further comprising a secondcontacting member provided at a position lower than the first contactingmember, the second contacting member being in contact with the stage,wherein the second contacting member is formed of a plurality ofmembers, each of the plurality of separate members being providedseparately.
 7. The placement apparatus according to claim 4, furthercomprising a second contacting member provided at a position lower thanthe first contacting member, the second contacting member being incontact with the stage, wherein the first contacting member and thesecond contacting member are electrically connected with each other viaat least one of the connecting member and the stage.
 8. The placementapparatus according to claim 4, wherein the connecting member isdisposed at a recess provided at an insulator ring, the insulator ringbeing disposed around a side surface of the edge ring and the stage; andthe first contacting member is disposed at a recess provided at theconnecting member, so as to be in contact with the outer circumferenceof the edge ring. 9-10. (canceled)
 11. The placement apparatus accordingto claim 4, wherein the first contacting member is an elastic conductivemember.
 12. The placement apparatus according to claim 4, wherein theconnecting member is fixed to the stage with a fixing member. 13.(canceled)
 14. The placement apparatus according to claim 4, furtherincluding an insulating member separating the stage into an innerportion and an outer portion electrically, wherein the outer portion isconfigured such that direct current voltage is applied to the outerportion.
 15. A processing apparatus comprising: a processing vesselincluding a processing space for applying a process to a workpiece; andthe placement apparatus according to claim 4, the placement apparatusbeing provided in the processing vessel.
 16. (canceled)